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We demonstrate a novel technique for direct measurement of the oscillation frequency in an optical-tweezers trap. The technique uses the phenomenon of parametric resonance in an oscillator when the stiffness of the trapping potential is modulated. The trapped particle is a strongly damped oscillator; hence, the signature of parametric resonance is not an increase in the amplitude but an increase in the size of Brownian fluctuations. The trap frequency is measured with an accuracy of 0.1%, which is better than previous techniques and thus opens up new possibilities in experiments with optical tweezers.

Paediatric age group is most vulnerable for the accidental foreign body (FB) ingestion which may go unnoticed. These patients present with symptoms or complications as a result of FB and may mimic other conditions on various investigations. We describe a 9-month old infant who ingested crystal gel ball and presented with vomiting for a month. On radiological imaging it was interpreted as duplication cyst of the duodenum. At operation, crystal gel ball was retrieved. Our case vindicates importance of keeping various possibilities in mind as differential diagnoses during evaluation and management of surgical ailments such as the duplication cyst of duodenum.

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